1. Field of the Invention
The present invention concerns the fields of molecular medicine and targeted delivery of therapeutic agents. More specifically, the present invention relates to compositions and methods for identification and use of peptides that selectively target white adipose tissue and placenta in vivo or in vitro. In other embodiments, the invention concerns compositions and methods for screening potential teratogenic agents.
2. Description of Related Art
Phage display is a technique in which a phage library expresses, for example, a set of random peptide sequences of defined length, incorporated into a phage coat protein (e.g., Smith and Scott, Science 228:1315-17, 1985; Smith and Scott, Meth. Enzymol. 21:228-57, 1993). Peptide sequences that bind to a target molecule, cell, tissue or organ may be identified by incubating a phage display library with the target and selecting for bound peptides (biopanning) (e.g., Pasqualini and Ruoslahti, Nature 380:364-66, 1996; Arap et al., Science 279:377-80, 1998a). Unbound phage may be washed away and bound phage eluted and collected. The collected phage may be amplified and taken through further binding/amplification cycles to enrich the pool of peptides for those that selectively and/or specifically bind to the target. With each cycle, the proportion of phage in the pool that contain targeting peptides for the target of interest is enriched. After several cycles, individual phage clones may be characterized by DNA sequencing to identify the targeting peptide sequences.
Targeting peptides that exhibit selective and/or specific binding for placenta or adipose tissues have not been previously reported in the literature. Targeting peptides against placenta or adipose tissues would have a variety of potential uses. Targeting peptides against adipose tissue could be used to control obesity and related conditions. Adipose-targeting peptides would also be of potential use to treat HIV related adipose malformations such as lipodystrophia and/or hyperlipidemia (see, e.g., Zhang et al., J. Clin. Endocrin. Metab. 84:4274-77, 1999; Jain et al., Antiviral Res. 51:151-177, 2001; Raolin et al., Prog. Lipid Res. 41:27-65, 2002). Targeting peptides against placental tissue could be used to reduce harmful effects by tetragenic agents, to deliver therapeutic agents to the placenta and/or the fetus and to induce labor or spontaneous abortion. Placental receptors identified through the use of placental targeting peptides could be used to screen for potential teratogens.
Presently available methods for control of weight include dieting and surgical procedures. These often exhibit adverse effects and may not result in long-term weight loss. Dieting includes both popular (fad) diets and the use of weight loss and appetite supplements. Fad diets are only good for short-term weight loss and do not achieve long-term weight control. They are often unhealthy, since many important nutrients are missing from the diet. In addition, rapid weight loss can result in dehydration. After losing weight, the dieters typically return to their original eating habits. This often results in weight gain that can exceed the subject's weight before dieting (yo yo effect).
Appetite suppressants such as Phentermen HCl, Meridia, Xernical, Adipex-P, Bontril and Ionomin may have adverse effects, such as addiction, dry mouth, nausea, irritability, and constipation. These supplements can also lead to more serious problems like eating disorders. Weight control through use of such supplements is ineffective, with only limited weight loss achieved. Effective drugs for controlling weight, such as fenfluramine, were withdrawn from the market due to cardiotoxicity.
Surgical methods for weight reduction, such as liposuction and gastric bypass surgery, have many risks. Liposuction removes subcutaneous fat through a suction tube inserted into a small incision in the skin. Risks and complications may include scarring, bleeding, infection, change in skin sensation, pulmonary complications, skin loss, chronic pain, etc. In gastric bypass surgery, the patient has to go through the rest of his or her life with a drastically altered stomach that can hold just two or three ounces of food. Side effects may include nausea, diarrhea, bleeding, infection, bowel blockage caused by scar tissue, hernia and adverse reactions to general anesthesia. The most serious potential risk is leakage of fluid from the stomach or intestines, which may result in abdominal infection and the need for a second surgery. None of the presently available methods for weight control is satisfactory and a need exists for improved methods of weight loss and control.
Another adipose related disease state is lipodystrophy syndrome(s) related to HIV infection (e.g., Jain et al., Antiviral Res. 51:151-177, 2001). Mortality rates from HIV infection have decreased substantially following use of highly active antiretroviral therapy (HAART) (Id.) However, treatment with protease inhibitors as part of the HAART protocol appears to result in a number of lipid-related symptoms, such as hyperlipidemia, fat redistribution with accumulation of abdominal and cervical fat, diabetes mellitus and insulin resistance (Jain et al., 2001; Yanovski et al., J. Clin. Endocrin. Metab. 84:1925-1931; Raulin et al., Prog. Lipid Res. 41:27-65, 2002). Although of minor significance compared to the underlying HIV infection and possible development of AIDS related complex (ARC) and/or AIDS, lipodystrophy syndrome adversely affects quality of life and may be associated with increased risk of coronary artery disease, heart attack, stroke and other adverse side affects of increased blood lipids. While treatment with metformin, an insulin-sensitizing aget, has been reported to provide some alleviation of symptoms (Hadigan et al., J. Amer. Med. Assn. 284:472-477, 2000), a need exists for more effective methods of treating HIV related lypodystrophy.
Teratogens fall into two classes. The first class includes compounds that are actively or passively transferred through the materno-fetal barrier. Those target fetal development by altering cell-signaling pathways that control essential processes in the developing embryo, such as angiogenesis (D'Amato, R. J., et al 1994. Proc. Natl. Acad. Sci. USA 91: 40824085; Funnell, R. H. 1999. J. Allergy Clin. Immunol. 103:337-342).
Teratogens of the second class interfere with fetal development by affecting the delivery of nutrients to the embryo through the placenta (Maranghi, F., et al. 1998. Adv. Exp. Med. Biol. 444: 129-136; Rugh, R. 1990. The Mouse: Its Reproduction and Development, Oxford Science Publications, Oxford). Materno-fetal molecule exchange occurs by filtration of blood from the maternal to the fetal side of the placenta through several distinct cell layers. Teratogens that target the placenta are thought to function by blocking receptors required for transport of nutrients to the fetus (Beckman, D. A., et al. 1990. Teratology 41: 395-404). Present methods of treatment primarily involve avoiding exposure of the pregnant woman to teratogens. Such methods are ineffective where the mother is unaware of her pregnancy, or for novel teratogens whose effect on fetal development have not yet been characterized. Because teratogens are identified by in vivo animal testing, differences in placental receptors between humans and test animals, such as mice, may result in the failure to identify teratogenic effects until multiple birth defects are reported, such as in the thalidomide tragedy. A need exists for methods of identifying the placental receptors for teratogens, in order to allow more accurate teratogen screening procedures.